An understanding of the biological basis of the neuroimmune mechanism is essential for establishing the relationship between behavior and immunity. Current evidence indicates both the opioid neuropeptides and the circulating biological fluid have multifunctional roles in the neuroimmune mechanism. The opioid neuropeptides are used as bidirectional signal molecules by all three systems in the mechanism. The circulating biological fluid is serving as the medium for the immunocytes and as the carrier for the signal molecules. The object of this comparative study is to examine the functions and fate of opioid neuropeptides in the circulating biological fluids of invertebrates and vertebrates with the goal of gaining a better understanding of their roles in the neuroimmune mechanism. Studies will be carried out in five areas. 1) HPLC-RIA will be used to detect known opioid neuropeptides in hemolymph and plasma. Neuroimmunologically active materials in HPLC fractions of these fluids will be assayed by their effects on immunocyte activities, lymphocyte proliferation and electrophysiological response of Aplysia neurons. Attempts will be made to isolate the active materials. 2) RIA activities in the fluids before and after enzyme treatment will be used to determine the presence of opioid precursor. Attempts will be made to isolate the precursors and to determine the processing pathway. 3) Non-oxidizing extraction procedure will be developed to determine if Met-enkephalin sulfoxide exists endogenously. The possible oxidation of Met-enkephalin by superoxide from lymphocytes will be tested. 4) Degradation of ME by hemolymph and plasma will be studied in regard to the pattern of degradation and the enzymes involved. 5) The effects of stress on the functions and fate of opioid neuropeptides in hemolymph will be used to examine the relationship between psychological and physiological states.